A grid-connected converter mainly converts DC power generated by solar power, into AC power that is synchronous to AC power of supply mains, and the grid-connected converter merges its AC power with the AC power of the supply mains to supply a load. Most grid-connected converters nowadays employ semiconductor switch components to perform bipolar sinusoidal pulse width modulation to convert input DC power into output AC power. After receiving switching signals, the semiconductor switch components usually take a delay time to completely be switched on or off.
In the case of a first switch module and a second switch module carried out by upper and lower semiconductor switch components of a bridge arm respectively, the first switch module and the second switch module take terms being switched on. In other words, when the first switch module is switched off, the second switch module will be switched on. When the second switch module is switched off, the first switch module will be switched on.
When the first switch module becomes off but the second switch module becomes on or when the first switch module becomes on but the second switch module becomes off, the semiconductor switch components need the delay time from receiving driving signals to actual action, and the delay time is varied with the material and fabrication process of semiconductor switch components. Since the duration of switching off the semiconductor switch components is longer than the duration of switching on the semiconductor switch components, the first switch module and the second switch module may simultaneously be switched on, resulting in the short-circuit to the grid-connected converter.
In order to prevent the first switch module and the second switch module from being switched on at the same time, a dead time period is set when some of the semiconductor switch components are being switched on and the other semiconductor switch components are being switched off. The dead time period is used for buffering the above delay time and is set according to the delay time.
However, during the dead time period, the grid-connected converter will have output voltage loss that distorts the output voltage waveform and weakens the grid-connected converter's performance.